Decomposition and Vibrational Relaxation in CH<sub>3</sub>I and Self-Reaction of CH<sub>3</sub> Radicals YangXueliang GoldsmithC. Franklin TranterRobert S. 2009 Vibrational relaxation and dissociation of CH<sub>3</sub>I, 2−20% in krypton, have been investigated behind incident shock waves in a diaphragmless shock tube at 20, 66, 148, and 280 Torr and 630−2200 K by laser schlieren densitometry. The effective collision energy obtained from the vibrational relaxation experiments has a small, positive temperature dependence, ⟨Δ<i>E</i>⟩<sub>down</sub> = 63 × (<i>T</i>/298)<sup>0.56</sup> cm<sup>−1</sup>. First-order rate coefficients for dissociation of CH<sub>3</sub>I show a strong pressure dependence and are close to the low-pressure limit. Restricted-rotor Gorin model RRKM calculations fit the experimental results very well with ⟨Δ<i>E</i>⟩<sub>down</sub> = 378 × (<i>T</i>/298)<sup>0.457</sup> cm<sup>−1</sup>. The secondary chemistry of this reaction system is dominated by reactions of methyl radicals and the reaction of the H atom with CH<sub>3</sub>I. The results of the decomposition experiments are very well simulated with a model that incorporates methyl recombination and reactions of methylene. Second-order rate coefficients for ethane dissociation to two methyl radicals were derived from the experiments and yield <i>k</i> = (4.50 ± 0.50) × 10<sup>17</sup> exp(−32709/<i>T</i>) cm<sup>3</sup> mol<sup>−1</sup> s<sup>−1</sup>, in good agreement with previous measurements. Rate coefficients for H + CH<sub>3</sub>I were also obtained and give <i>k</i> = (7.50 ± 1.0) × 10<sup>13</sup> exp(−601/<i>T</i>) cm<sup>3</sup> mol<sup>−1</sup> s<sup>−1</sup>, in reasonable agreement with a previous experimental value.